Torque converter

ABSTRACT

A torque converter is provided with an impeller and a cover, fixed to one another and configured for attachment to a drive member. A turbine is rotationally mounted between the impeller and the cover and is configured for attachment to a driven member. A lockup clutch is provided to lock the impeller and cover to the turbine when a fluid pressure applied to the lockup clutch increases above a torque converter lockup pressure. The lockup clutch may include a clutch-pack having rings that are splined to the piston or to the cover via tabs. The flanks of the tabs and their corresponding lugs may be substantially radial, or the flanks of the tabs or lugs may be parallel to one another. The cover may be formed from a base plate and a cylindrical wall piece. A plurality of lugs may be formed around the periphery of the base plate, and ones of the tabs may be splined thereto.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This patent application claims priority to U.S. provisionalpatent application entitled “Torque Converter” of Clint D. Cannon, Ser.No. 60/380,097, filed on May 2, 2002, which is hereby incorporated byreference for all that it discloses.

BACKGROUND

[0002] A vehicle with an automatic transmission requires a torqueconverter to vary the transfer of torque between the vehicle's engineand transmission. Without a torque converter, a vehicle with anautomatic transmission would be unable to keep its engine running whilestopped, and would lurch forward (i.e., at the engine's speed) when putinto gear.

[0003] At idle and low vehicle speeds, components of a torque converterrotate at different speeds (i.e., some components are fixed to theengine and rotate at engine speed, and other components are fixed to thetransmission and rotate at less than engine speed or not at all). As atorque converter transfers more and more torque between a vehicle'sengine and transmission, a point is reached where all components of atorque converter rotate at or about the same speed. When this point isreached, it is typically desirable to “lock” the components of thetorque converter to one another. When in “lockup”, a torque convertertransfers 100% of an engine's torque to a vehicle's transmission,despite small (and sometimes moderate) changes in an engine's speed.

[0004] Torque converter lockup is governed by a lockup clutch. Given theoften extreme torsional forces that a lockup clutch is subjected to, itsdesign is critical to the effectiveness and longevity of a torqueconverter.

SUMMARY OF THE INVENTION

[0005] One aspect of the invention is embodied in a torque convertercomprising an impeller, a cover, a turbine, and a lockup clutch. Theimpeller and cover are fixed to one another and configured forattachment to a drive member, and the cover has a plurality of lugs on asurface thereof facing the impeller. The turbine is rotationally mountedbetween the impeller and the cover and is configured for attachment to adriven member. The lockup clutch comprises a piston and a clutch-pack.The piston is splined to and rotates with the turbine, between theturbine and the cover. The clutch-pack comprises first and second rings.The first ring is splined to and rotates with the piston. The secondring is positioned between the first ring and the piston and comprises aplurality of outwardly facing tabs splined to the plurality of lugs onthe cover. As a fluid pressure between the turbine and the pistonincreases above a torque converter lockup pressure, the piston, ringsand cover frictionally engage one another. In one variant of thisembodiment, at least some of the outwardly facing tabs and theircorresponding lugs comprise substantially radial flanks. In anothervariant of this embodiment, at least some of the outwardly facing tabscomprise parallel flanks, and flanks of the lugs corresponding theretofollow contours of the tabs.

[0006] Another aspect of the invention is embodied in a torque convertercomprising an impeller, a cover, a turbine, and a lockup clutch. Theimpeller and cover are fixed to one another and configured forattachment to a drive member. The turbine is rotationally mountedbetween the impeller and the cover and is configured for attachment to adriven member. The lockup clutch comprises a piston and a clutch-pack.The piston is splined to and rotates with the turbine, between theturbine and the cover. The piston comprises a plurality of lugs on asurface of the piston facing the cover. The clutch-pack comprises firstand second rings. The first ring is splined to and rotates with thecover. The second ring is positioned between the first ring and thecover and comprises a plurality of inwardly facing tabs splined to theplurality of lugs on the piston. As a fluid pressure between the turbineand the piston increases above a torque converter lockup pressure, thepiston, rings and cover frictionally engage one another. In one variantof this embodiment, at least some of the inwardly facing tabs and theircorresponding lugs comprise substantially radial flanks. In anothervariant of this embodiment, at least some of the inwardly facing tabscomprise parallel flanks, and flanks of the lugs corresponding theretofollow contours of the tabs.

[0007] Yet another aspect of the invention is embodied in a torqueconverter comprising a base plate, a cylindrical wall piece, animpeller, a turbine, and a lockup clutch. The base plate is configuredfor attachment to a drive member and comprises a plurality of lugsaround the periphery thereof. At least some of the lugs comprisestraight flanks. The cylindrical wall piece is fixed to the base plate,and the impeller is fixed to the cylindrical wall piece. The turbine isrotationally mounted between the impeller and the cover and isconfigured for attachment to a driven member. The lockup clutch servesto lock the impeller and cover to the turbine when a fluid pressureapplied to the lockup clutch increases above a torque converter lockuppressure.

[0008] Other embodiments of the invention are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Illustrative embodiments of the invention are illustrated in thedrawings, in which:

[0010]FIG. 1 is a perspective view of an exemplary torque converter;

[0011]FIG. 2 illustrates a first exploded view of the FIG. 1 torqueconverter;

[0012]FIG. 3 illustrates a second exploded view of the FIG. 1 torqueconverter;

[0013]FIG. 4 illustrates a first lockup clutch ring of the FIG. 1 torqueconverter;

[0014]FIG. 5 illustrates a second lockup clutch ring of the FIG. 1torque converter;

[0015]FIGS. 6 & 7 illustrate the tab and lug design of the FIG. 1 torqueconverter;

[0016]FIGS. 8 & 9 illustrate a first alternative to the tab and lugdesign illustrated in FIGS. 6 & 7;

[0017] FIGS. 10 illustrates a second alternative to the tab and lugdesign illustrated in FIGS. 6 & 7;

[0018]FIGS. 11 & 12 illustrate an exemplary two-piece embodiment of thetorque converter cover shown in FIGS. 2 & 3.

DETAILED DESCRIPTION OF THE INVENTION

[0019] A torque converter 100 is generally illustrated in FIGS. 1-3. Thetorque converter 100 comprises an impeller 102, a cover 104, a turbine106, a lockup clutch 108, and (optionally, but desirably) a stator 110.The impeller 102 and cover 104 are fixed to one another (i.e., pressfitted and/or welded) and are configured for attachment to a drivemember 112 (e.g., an engine crankshaft or flywheel). The turbine 106 isrotationally mounted between the impeller 102 and the cover 104 and isconfigured for attachment to a driven member 114 (e.g., an automatictransmission input shaft). The lockup clutch 108 is generally positionedbetween the turbine 106 and the cover 104, and has components splineddirectly or indirectly to both the turbine 106 and the cover 104. Thestator 110 is positioned between the impeller 102 and the turbine 106.

[0020] By way of example, FIG. 3 shows that a drive member 112 may beattached to the cover 104, and a driven member 114 may be attached tothe turbine 106 (by means of an axial hole provided in the impeller 102.Alternately, the drive member 112 could be attached to the impeller 102,and the driven member 114 could be attached to the turbine 106 via ahole in the cover 104.

[0021] The lockup clutch 108 comprises a piston 116 and a clutch-pack118. The piston is located between the turbine 106 and the cover 104 andis splined to (and rotates with) the turbine 106. The clutch-packcomprises first and second rings 120, 122, the first of which is splinedto (and rotates with) the piston 116. The second of the rings ispositioned between the first ring 120 and the piston 116 and is splinedto (and rotates with) the cover 104.

[0022] When filled with a viscous fluid 124 (e.g., automatictransmission fluid (ATF)), and upon start of a vehicle's engine, thetorque converter 100 operates as follows. First, drive member 112 beginsto turn at engine speed. Consequently, cover 104 turns at engine speed,and impeller 102 turns at engine speed. The rotation of impeller 102about the axis of drive member 112 causes the impeller 102 to pump fluid124 into the turbine 106.

[0023] As the impeller 102 pumps fluid into the turbine 106, an engine'spower is transferred from the impeller 102 to the turbine 106 via thefluid 124, and the turbine 106 transfers power to a vehicle'stransmission via the transmission's input shaft 114. Finally, a vehiclebegins to move. But for the stator 110, however, a vehicle would beginto move at a relatively slow rate.

[0024] When a driver accelerates from a stop, or accelerates at lowvehicle speeds, the rotational speed of the impeller 102 is greater thanthe rotational speed of the turbine 106. During these low vehiclespeeds, the stator 110 redirects fluid 124 as it returns from theturbine 106 so that the direction of the fluid 124 is changed back tothat of the impeller 102. The stator 110 is mounted on a one-way clutchthat allows it to rotate with the direction of the engine, but notagainst engine rotation. The one-way clutch locks the stator 110 whenthe impeller 102 is turning faster than the turbine 106, and the stator110 redirects fluid flow over the stator vanes in an outward radialdirection to increase the amount of engine torque transferred betweenthe impeller 102 and the turbine 106 (i.e., the stator 110 serves as atorque transfer multiplier). The amount of torque multiplicationprovided by a stator 110 is controlled by the shape of the stator vanes.

[0025] When the speed of a torque converter's turbine 106 is equal to(or approximately equal to) the speed of the torque converter's impeller102, the stator 110 freewheels on its shaft so that fluid flow from theturbine 106 to the impeller 102 is restricted as little as possible,thereby improving torque converter efficiency.

[0026] When the speed of a torque converter's turbine 106 is equal to(or approximately equal to) the speed of the torque converter's impeller102, the torque converter 100 transfers a vehicle's maximum enginetorque to the vehicle's transmission (and with a well designedtransmission, to the vehicle's wheels). When this occurs, it istypically desirable to hold this state absent a driver's consciousdecision to significantly decelerate his or her vehicle. In other words,it is typically desirable to hold a maximum torque transfer statethrough small (and possibly even moderate) changes in a vehicle's enginespeed. Given the difficultly in maintaining the fluid 124 in a constantstate, something more is typically required to “lock” the rotationalspeeds of a torque converter's impeller 102 and turbine 106. Thissomething more is provided by a lockup clutch 108.

[0027] Referring to FIG. 3, one sees that the lockup clutch 108comprises a piston 116 and a clutch-pack 118. The clutch-pack 118, inturn, comprises first and second rings 120, 122. The first ring 120comprises a plurality of inwardly facing tabs (e.g., tabs 400, 402; FIG.4) that are splined to lugs on the piston 116 (see, e.g., tab 400 andlug 600 in FIG. 6). The second ring 122 comprises a plurality ofoutwardly facing tabs (e.g., tabs 500, 502; FIG. 5) that are splined tolugs on the cover 104 (see, e.g., tab 500 and lug 700 in FIG. 7).

[0028] As the impeller 102 directs fluid toward the turbine 106, theturbine 106 moves toward the cover 104, and a fluid pressure between theturbine 106 and the piston 116 gradually increases. As the pressureagainst the piston 116 increases, the piston 116, rings 120, 122 andcover 104 are compressed toward one another; and, above a torqueconverter lockup pressure, the piston 116, rings 120, 122 and cover 104frictionally engage one another and “lock”. Fluid 124 that is trappedbetween the piston 110 and the cover 104 escapes through the shaft ofdriven member 114. Prior to lockup, fluid 124 flows between the matingsurfaces of the cover 104, rings 120, 122 and piston 116 so as tolubricate them as they are compressed together.

[0029] Preferably, each of the rings 120, 122 is provided with one ormore friction linings 126, 128, 130. By way of example, FIG. 3 shows thefirst ring 120 having a friction lining 126 on a side thereof adjacentthe cover 104, and shows the second ring 122 having friction linings128, 130 on opposite sides thereof. The cover 104, piston 116 andunlined side of ring 120 comprise clutch surfaces for the frictionlinings 126-130 to bear against when the piston, rings and coverfrictionally engage one another. In this manner, three frictionalcouplings are created: one between the first ring 120 and the cover 104,one between the first and second rings 120, 122, and one between thesecond ring 122 and the piston 116.

[0030] Note that depending on the composition and texture of the variousclutch surfaces, the friction linings 126-130 might not be needed.Furthermore, the friction linings 126-130 could be otherwise distributedamong the rings, or even applied to the cover and piston. However,applying the friction linings 126-130 to the rings 120, 122 tends to beeasier given current manufacturing processes.

[0031] When the torque converter 100 is not in lockup (typically duringengine start, during vehicle acceleration from a stop, and duringvehicle acceleration at low speeds), the rings 120, 122 of theclutch-pack 118 are subjected to extreme torsional forces. Not only arethe rings 120, 122 subjected to broad changes in torsional forces (e.g.,as the rotational speed of an engine's crankshaft varies during vehicleacceleration and deceleration), but the rings 120, 122 are alsosubjected to rapid changes in torsional forces as brief pauses betweenfirings of an engine's cylinders (and even vehicle vibrations) areimparted to the rings 120, 122. These torsionals often lead to prematurewear and peaning of the tabs 400, 402, 500, 502 and lugs 600, 700 shownin FIGS. 4-7 and, eventually, to premature failure of a vehicle's torqueconverter 100. Transmission failure is also possible (i.e., due to thesharing of fluid 124 impregnated with metal filings between the torqueconverter 100 and transmission).

[0032] To lessen the wear and peaning of tabs 400, 402, 500, 502 andlugs 600, 700, the leading and trailing flanks 410, 412, 510, 512, 602,604, 702, 704 (or sides) of at least some (and preferably all) of thetabs and lugs are designed to be substantially radial. See FIGS. 4-7.That is, the tabs 400, 500 and lugs 600, 700 may be provided with flanks410, 602, 510, 702 that are substantially parallel to radial lines 408,508 extending outward from the centers of the rings 120, 122, cover 104and piston 110 (the radial lines of which should all coincide with acommon axis or center). Although it is preferable that a tab's or lug'sentire flank 410, 602, 510, 702 be radial (as shown in FIGS. 6 & 7), oneembodiment of the invention allows the flanks 802, 804, 808, 810, 902,904, 908, 910 of tabs 800, 900 and lugs 806, 906 to merely be“substantially” radial. For example, and as shown in FIGS. 8 & 9, thedistal portions of tabs 800, 900 (and spaces between lugs) could berounded, so long as the majorities of each tab's or lug's flanks 802,804, 808, 810, 902, 904, 908, 910 are substantially radial.

[0033] For purposes of this description, “substantially radial” flanksare defined to include those flank orientations falling between those ofa tab with parallel flanks, and those of a lug with parallel flanks.Therefore, a substantially radial flank in FIG. 6 could vary between theflank orientations denoted by lines 606 and 608. Likewise, asubstantially radial flank in FIG. 7 could vary between the flankorientations denoted by lines 706 and 708.

[0034] When a ring's tabs (400 or 500) are provided with substantiallyradial flanks (410/412 or 510/512), and the lugs 600, 700 correspondingthereto are provided with substantially radial flanks (e.g., flanks 602and 702), the ring (120 or 122) operates as efficiently as possible intransferring torque within a torque converter 100. Efficient torquetransfer means a clutch-pack's rings 120, 122 absorb fewer of thetorsionals imparted thereto, and the torsionals are instead absorbed bythe cover and piston (which have a greater mass and rigidity forabsorbing the torsionals). As a result, the tab and lug designillustrated in FIGS. 2-7 subjects a clutch pack's rings 120, 122 to lesswear and peaning.

[0035] The tabs and lugs illustrated in FIGS. 2-7 are also beneficial inthat they largely maintain their radial engagement as they wear (unliketabs and lugs having generally roundish flanks, that tend to lose theirsnug fit as they wear). For example, refer to the tab and lugarrangement shown in FIG. 7. As a result of the radial engagementbetween flanks 510 and 702, and the similar radial engagement of allother flanks on ring 122, the flanks tend to wear evenly and maintaintheir radial engagement. Furthermore, even if the inner and outercircumferences of the ring 122 wear (or if the circumferences do not fitsnugly to their mating surfaces when a torque converter 100 is firstassembled), and the ring 122 begins to sag (i.e., as a result of thetorque converter 100 having a horizontal axis of rotation and the ringshaving vertically aligned faces), the flanks 510 and 702 will stillengage radially and tend to wear at a uniform rate.

[0036] In an alternate tab and lug design (1000, 1006; FIG. 10), theflanks 1002, 1004 of tabs (e.g., tab 1000) or lugs (not shown) aredesigned to be parallel to one another, thus resulting in generallysquare tabs or lugs. Although they do not transfer torque as efficientlyas tabs and lugs with radial flanks, tabs and lugs comprising parallelflanks still transfer torque more efficiently than tabs and lugscomprising generally rounded flanks.

[0037] Given that the tab and lug arrangements illustrated in FIGS. 410are designed to transfer a greater number of torsional forces to thecover 104 and piston 110, the cover and piston need to have a sufficientmass and rigidity to absorb the torsional forces that will be applied tothem. In one embodiment of the torque converter 100, the cover 104 andpiston 110 are formed of billet steel.

[0038] Although there are many ways to cut radial or square tabs andlugs from a torque converter's cover 104, piston 110 and rings 120, 122,cutting radial or square lugs in a torque converter's cover 104 isdifficult. Typically, lugs are cut in a torque converter's cover bymeans of drilling or milling. However, such operations make it difficultto produce straight flanks (e.g., radial or square flanks). This isbecause large drill bits and milling cutters produce too great of“rounds” at the corners of a lug, and small drill bits and millingcutters require too many repetitions or passes to make cover manufacturepractical. FIGS. 11 & 12 therefore illustrate a two-piece cover 104. Thecover 104 comprises a base plate 1100 and a cylindrical wall piece 1102.In this manner, lugs 700 having straight flanks may be milled orotherwise formed in the base plate 1100 prior to fixing the base plate1100 to the cylindrical wall piece 1102. Byway of example, the baseplate 1100 and cylindrical wall piece 1102 may be press fitted together,and then welded. Depending on the process used to press the two piecestogether, one or both of the pieces may be heated to enable an easierfit.

[0039] If lugs are formed in a cover 104 as described in the precedingparagraph, the tabs 500, 502 of a clutch-pack ring 122 may extend towithin a few thousandths of an inch from the wall of the cover 104.

[0040] While illustrative and presently preferred embodiments of theinvention have been described in detail herein, it is to be understoodthat the inventive concepts may be otherwise variously embodied andemployed, and that the appended claims are intended to be construed toinclude such variations, except as limited by the prior art.

What is claimed is:
 1. A torque converter, comprising: a) an impellerand a cover, fixed to one another and configured for attachment to adrive member; the cover having a plurality of lugs on a surface thereoffacing the impeller; b) a turbine, rotationally mounted between theimpeller and the cover and configured for attachment to a driven member;and c) a lockup clutch, comprising: i) a piston, splined to and rotatingwith the turbine between the turbine and the cover; and ii) aclutch-pack comprising a first ring that is splined to and rotates withthe piston, and a second ring that is positioned between the first ringand the piston; the second ring comprising a plurality of outwardlyfacing tabs splined to the plurality of lugs on the cover; at least someof the outwardly facing tabs and their corresponding lugs comprisingsubstantially radial flanks; wherein the piston, rings and coverfrictionally engage one another as a fluid pressure between the turbineand the piston increases above a torque converter lockup pressure. 2.The torque converter of claim 1, wherein at least some of the outwardlyfacing tabs and their corresponding lugs comprise radial flanks.
 3. Thetorque converter of claim 1, wherein the piston has a plurality of lugson a surface thereof facing the second ring, and wherein the first ringhas a plurality of inwardly facing tabs splined to the plurality of lugson the piston.
 4. The torque converter of claim 3, wherein at least someof the inwardly facing tabs and their corresponding lugs comprisesubstantially radial flanks.
 5. The torque converter of claim 3, whereinat least some of the inwardly facing tabs and their corresponding lugscomprise radial flanks.
 6. The torque converter of claim 1, wherein thefirst ring comprises a friction lining on a side thereof adjacent thecover, wherein the second ring comprises friction linings on oppositesides thereof, and wherein the cover, piston and unlined side of thefirst ring each comprise clutch surfaces for friction linings of thefirst and second rings to bear against when the piston, rings and coverfrictionally engage one another.
 7. The torque converter of claim 1,wherein: a) the cover comprises a base plate and a cylindrical wallpiece that are fixed to one another; and b) the lugs on the cover areformed on the base plate.
 8. The torque converter of claim 7, whereinthe cover is formed of billet steel.
 9. A torque converter, comprising:a) an impeller and a cover, fixed to one another and configured forattachment to a drive member; b) a turbine, rotationally mounted betweenthe impeller and the cover and configured for attachment to a drivenmember; and c) a lockup clutch, comprising: i) a piston, splined to androtating with the turbine between the turbine and the cover, and havinga plurality of lugs on a surface thereof facing the cover; and ii) aclutch-pack comprising a first ring that is splined to and rotates withthe cover, and a second ring that is positioned between the first ringand the cover; the second ring comprising a plurality of inwardly facingtabs splined to the plurality of lugs on the piston; at least some ofthe inwardly facing tabs and their corresponding lugs comprisingsubstantially radial flanks; wherein the piston, rings and coverfrictionally engage one another as a fluid pressure between the turbineand the piston increases above a torque converter lockup pressure. 10.The torque converter of claim 9, wherein at least some of the inwardlyfacing tabs and their corresponding lugs comprise radial flanks.
 11. Thetorque converter of claim 9, wherein the first ring comprises frictionlinings on opposite sides thereof, wherein the second ring comprises afriction lining on a side thereof adjacent the cover, and wherein thepiston, cover and unlined side of the first ring each comprise clutchsurfaces for friction linings of the first and second rings to bearagainst when the piston, rings and cover frictionally engage oneanother.
 12. A torque converter, comprising: a) an impeller and a cover,fixed to one another and configured for attachment to a drive member;the cover having a plurality of lugs on a surface thereof facing theimpeller; b) a turbine, rotationally mounted between the impeller andthe cover and configured for attachment to a driven member; and c) alockup clutch, comprising: i) a piston, splined to and rotating with theturbine between the turbine and the cover; and ii) a clutch-packcomprising a first ring that is splined to and rotates with the piston,and a second ring that is positioned between the first ring and thepiston; the second ring comprising a plurality of outwardly facing tabssplined to the plurality of lugs on the cover; at least some of theoutwardly facing tabs comprising parallel flanks, and flanks of the lugscorresponding thereto following contours of the tabs; wherein thepiston, rings and cover frictionally engage one another as a fluidpressure between the turbine and the piston increases above a torqueconverter lockup pressure.
 13. The torque converter of claim 12, whereinthe outwardly facing tabs comprising parallel flanks are square.
 14. Thetorque converter of claim 12, wherein: a) the piston has a plurality oflugs on a surface thereof facing the second ring; b) the first ring hasa plurality of inwardly facing tabs splined to the plurality of lugs onthe piston; and c) at least some of the inwardly facing tabs compriseparallel flanks, and flanks of the lugs corresponding thereto followcountours of the tabs.
 15. The torque converter of claim 14, wherein theinwardly facing tabs comprising parallel flanks are square.
 16. Thetorque converter of claim 12, wherein the first ring comprises afriction lining on a side thereof adjacent the cover, wherein the secondring comprises friction linings on opposite sides thereof, and whereinthe cover, piston and unlined side of the first ring each compriseclutch surfaces for friction linings of the first and second rings tobear against when the piston, rings and cover frictionally engage oneanother.
 17. The torque converter of claim 12, wherein: a) the covercomprises a base plate and a cylindrical wall piece that are fixed toone another; and b) the lugs on the cover are formed on the base plate.18. The torque converter of claim 17, wherein the cover is formed ofbillet steel.
 19. A torque converter, comprising: a) an impeller and acover, fixed to one another and configured for attachment to a drivemember; b) a turbine, rotationally mounted between the impeller and thecover and configured for attachment to a driven member; and c) a lockupclutch, comprising: i) a piston, splined to and rotating with theturbine between the turbine and the cover, and having a plurality oflugs on a surface thereof facing the cover; and ii) a clutch-packcomprising a first ring that is splined to and rotates with the cover,and a second ring that is positioned between the first ring and thecover; the second ring comprising a plurality of inwardly facing tabssplined to the plurality of lugs on the piston; at least some of theinwardly facing tabs comprising parallel flanks, and flanks of the lugscorresponding thereto following contours of the tabs; wherein thepiston, rings and cover frictionally engage one another as a fluidpressure between the turbine and the piston increases above a torqueconverter lockup pressure.
 20. The torque converter of claim 19, whereinthe inwardly facing tabs comprising parallel flanks are square.
 21. Thetorque converter of claim 19, wherein the first ring comprises frictionlinings on opposite sides thereof, wherein the second ring comprises afriction lining on a side thereof adjacent the cover, and wherein thepiston, cover and unlined side of the first ring each comprise clutchsurfaces for friction linings of the first and second rings to bearagainst when the piston, rings and cover frictionally engage oneanother.
 22. A torque converter, comprising: a) a base plate configuredfor attachment to a drive member and comprising a plurality of lugsaround the periphery thereof; at least some of the lugs comprisingstraight flanks; b) a cylindrical wall piece fixed to the base plate; c)an impeller fixed to the cylindrical wall piece; d) a turbine,rotationally mounted between the impeller and the cover and configuredfor attachment to a driven member; and e) a lockup clutch to lock theimpeller and cover to the turbine when a fluid pressure applied to thelockup clutch increases above a torque converter lockup pressure.